WASHINGTON -- Plant-eating dinosaurs of different species may have herded together, to escape meat-eaters nearby, according to an analysis of 163 million-year-old dino footprints on a muddy coastal plain in England.
In a study appearing Friday in the journal Science, British researchers say that 40 tracks of dinosaur footprints hint at a life and death struggle between prey and hunter in the days when dinosaurs ruled the world.
The tracks suggest that large and lumbering plant eaters of different types -- some as long as 90 feet and weighing 10 tons or more -- walked together across an open tidal plain, perhaps fleeing for their lives.
These animals were all sauropods, but of different types.
On a nearby track, the researchers also found the footprints of the smaller, faster Megalosaurus, a toothy meat eater that may have been more than 60 feet long. The tracks were going the same direction at about the same time as the sauropods. The Megalosaurus was a theropod, the same family as Tyrannosaurus rex, a heavyweight carnivore that developed millions of years later.
"The theropods there suggests that they were tracking the sauropods," said Julia Day, a paleontologist at the University of Cambridge, England, and first author of the Science study.
Day said the tracks of the sauropods show they were miles from the nearest heavy growth of plants, which was unusual because it is believed the huge vegetarians required food almost constantly.
"Sauropods have to keep eating and yet they were far away from any vegetation," said Day.
"We believe the animals were either migrating or walked out there to get away from the predators."
The sauropods moved slowly, spread out and walking in the same direction, with each animal leaving a set of several footprints.
In one track, there are the small, shorter footfalls of a juvenile walking beside a much larger sauropod, Day said. This suggests a parent and child traveling together across that ancient muddy plain.
Day said that the herding of plant-eaters from different species is not unusual. In modern times in Africa, zebra and wildebeest commonly move together over the grasslands and across the rivers of Tanzania and Kenya.
"This is the first evidence of a multi-specie herd of dinosaurs moving together," she said. "If they were migrating, they may have been going to a new food source and to a nesting ground."
The plain where the animals moved was covered with a clay soil which baked hard in the sun and eventually turned to limestone, preserving the footprints. Day said the prints had to be made at approximately the same time because the area was daily covered with ocean tides.
The types and sizes of the animals could be identified by the shape, width and depth of the footprints, she said.
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